Analytical methods for estimating saturated hydraulic conductivity in a tile-drained field

Determination of field-scale hydraulic properties is required for many hydrologic predictions. Four analytical methods for determining the saturated hydraulic conductivity k on the field scale for a field drained by a network of parallel drains are considered. These methods, all derived from the Boussinesq equation, relate: (1) time rate of change of discharge to discharge; (2) relative discharge to time; (3) time rate of change of water table height to height; and (4) relative water table height to time. Though all four methods eliminate the need to know precisely the beginning time of the recession curve, which is in practice ambiguous, Methods (2) and (4) do not require taking time derivates of observations, which introduces noise. The mean field-scale k based on several recession events on two 1 ha fields using all methods was 4 m/d. This is near the median k of 5 m/d calculated from 40 soil cores taken at various depths within the same fields, but five times less than the mean k of the soil cores (20 m/d).